1. Field of the Invention
The present invention relates to a folded fin forming method, machine and folded fin obtained therefrom. The folded fin has a corrugated configuration and is particularly used in constructing a heat sink for dissipating heat generated by Integrate Circuits (ICs).
2. The Prior Art
Due to the increased consumption of power of ICs (particularly Central Processing Units (CPUs)), heat dissipation of these electronic components is becoming increasingly important. To solve this problem, heat sinks are mounted to contact the CPUs to absorb heat generated thereby and dissipate it into the surrounding air.
Referring to FIG. 1, a conventional heat sink 10 is constructed by alumium extrusion to have a number of heat dissipating fins 12. The heat sink 10 formed by this method is costly.
To lower the cost, a folded fin 22 having a corrugated configuration is made by stamping or roll forming a metal sheet (usually an aluminum sheet), as seen in FIG. 2. The folded fin 22 consists of a number of inverted U-shaped heat dissipating fins 23 and is fixed to a flat base plate 24 by epoxy or riveting to form a heat sink 20.
The heat sinks 10, 20 made in accordance with the prior art share a common disadvantage. Each of the heat dissipating fin 12, 23 cannot have an aspect ratio (H/W) larger than twelve, otherwise breakage of the fins 12, 23 will occur during manufacture of the heat sink 10 or the folded fin 22. The limited aspect ratio of the fins 12, 23 limits the available heat dissipating area per length unit of the heat sink 10, 20.
Moreover, referring to FIG. 3, in order to enhance the heat dissipating effectiveness of the folded fin 22, when producing the folded fin 22 by roll forming, a number of louvers 252 are defined in webs 25 of the heat dissipating fins 23. Due to the limitation of the forming direction of he roll forming, the louvers 252 can only be vertically defined in the webs 25. Although the louvers 252 can increase the heat dissipating area of the folded fin 22, the direction of arrangement of the louvers 252 is perpendicular to the direction of forced air flow through the heat sink. Thus, the enhanced effectiveness achievable by the provision of the louvers 252 is not as significant as horizontal louvers.
Hence, an improvement over the prior art heat sink is needed.
Accordingly, an objective of the present invention is to provide a method for forming a folded fin with a number of inverted U-shaped heat dissipating fins which can have an unlimited aspect ratio without breakage of webs thereof occurring during formation of the folded fin.
Another objective of the present invention is to provide a machine for forming a folded fin with a number of inverted U-shaped heat dissipating fins which can have an unlimited aspect ratio without breakage of the webs thereof occurring during formation of the folded fin.
A further objective of the present invention is to provide a folded fin with a number of inverted U-shaped heat dissipating fins each having an aspect ratio larger than twelve and preferably between twenty and forty.
Still another objective of the present invention is to provide a method for forming a folded fin with a number of inverted U-shaped heat dissipating fins each of which has right-angled comers so that when the folded fin is attached to a metallic base plate, a maximum contacting area exists therebetween.
Still a further objective of the present invention is to provide a method for forming a folded fin with a number of inverted U-shaped heat dissipating fins each defining a number of horizontal louvers in webs thereof (or wave-like structures having horizontal peaks) so that the heat dissipating effectiveness of the folded fin can be significantly enhanced.
To fulfill the above-mentioned objectives, according to one embodiment of the present invention, a method for forming a folded fin includes the following steps:
providing a horizontal metal strip;
forming a number of pairs of indents alternately in top and bottom faces of the strip;
clamping the strip with three folding tools, wherein a first tool clamps the strip between a first pair of indents in the top face of the strip, a second tool clamps the strip between a successive second pair of indents in the bottom face of the strip, and a third tool clamps the strip between a fuirther successive third pair of indents in the top face of the strip; and
moving the second and third tools toward the first tool to fold the strip to position where sections of the strip between the first and second tools, and the second and third tools are vertically bent, wherein the third tool moves horizontally toward the first tool and the second tool moves at an angle toward an upper side of the first tool.
A machine for forming the folded fin consists of a stationary frame, a folding tool carrier horizontally and reciprocally mounted on the frame, three folding tools carried by the carrier for folding a horizontal strip inserted in the machine into the folded fin, and a locating device for fixing the horizontal metal strip relative to the frame when the folding tools do not clamp the strip.
After he horizontal strip has been received in the machine, the three folding tools securely clamp the strip at an original position. The carrier horizontally displaces the three folding tools together with the strip a predetermined distance toward the first tool. Thereafter, the second tool moves at an angle toward an upper side of the first tool and the third tool moves horizontally toward the first tool to reach a position where sections of the strip between the first and second tools, and the second and third tools are vertically bent, thereby forming an inverted U-shaped heat dissipating fin. The locating device is driven to fix the strip relative to the frame. The three folding tools are released from the strip and the carrier displaces the folding tools a predetermined distance toward the third folding tool. The three folding tools return to their respective original positions and securely clamp the strip. Afterwards, the above operation is repeated to form successive inverted U-shaped heat dissipating fins on the strip thereby obtaining the folded fin.
In the machine according to the present invention, the three folding tools are spaced from each other a distance D when they are at the original position which is substantially equal to a height H of the formed inverted U-shaped heat dissipating fin (H=D+2t, t: thickness of the strip). Furthermore, each folding tool has a width d substantially equal to a width w of the formed heat dissipating fin (W=d+2t). Since during formation of the forded fin the machine in accordance with the present invention does not exert any stretching force on webs of the inverted U-shaped heat dissipating fins, theoretically, the folded fin in accordance with the present invention can have an unlimited aspect ratio without breakage occurring to the webs. In a preferred embodiment of the present invention, the folded fin has an aspect ratio between twenty and forty.
To facilitate the folding operation of the machine, a number of pairs of indents can be alternately defined in top and bottom faces of the strip. When the strip is received in the machine and the folding tools clamp the strip at their original position, the first tool clamps the strip between a fist pair of indents in the top face of the strip, the second tool clamps the strip between a successive second pair of indents in the bottom face of the strip, and the third tool clamps the strip between a further successive third pair of indents in the top face of the strip.
To enhance the heat dissipating effectiveness of the folded fin, when defining the indents in the strip, a number of slits can be defined between adjacent pairs of indents. The slits are defined parallel to the indents, whereby when the folded fin is formed a number of horizontal louvers are defined in the webs of the heat dissipating fins.
Alternatively, a wave-like structure can be formed between adjacent pairs of indents having peaks which are parallel to the indents whereby the folded fin is formed with the wave-like structure on the webs of the heat dissipating fins.